The only lake that springs to mind in Pembury is the one down Chalket Lane, (almost opposite Lower Green Road).
There are a couple of lakes down there, the main one on the right as you drive down has some decent sized carp in there, but if you carry on a bit further there are two smaller lakes and this is where the gate and concrete structure you mention are. There as some carp in the other smaller lakes, also some decent sized Perch as well.
I've fished all three many (many) years ago. I visited the main lake again a couple of years ago, as I say there are some decent carp in there but the place, unfortunately, is rat infested. Loads of rubbish left on the banks for them to dig around in. It was bad enough during the day, I certainly wouldn't want to be there after dark!!